LONDON (AFP) - US Secretary of State Hillary Clinton joined four European counterparts in London on Thursday to discuss possible tougher sanctions on Iran over its nuclear programme, a US official said. Clinton huddled with Britains David Miliband, Frances Bernard Kouchner, Germanys Guido Westerwelle and Italys Franco Frattini on the sidelines of a day-long international conference on Iraq. They discussed where things stand and possible next steps both in New York (at the UN Security Council) and with respect to greater implementation of existing measures, the official said. They also heard a short briefing from Stuart Levey, the US Treasurys under-secretary for terrorism and financial intelligence, the official said on condition of anonymity. Hillary said Irans stance on its nuclear programme is leaving major powers with little choice but to apply further pressure on the Islamic republic. Iran has provided a continuous stream of threats to intensify its violation of international nuclear norms, Clinton told reporters in London where she attended a day-long international conference on Afghanistan. Irans approach leaves us with little choice than to work with our partners to apply greater pressure in the hopes that it will cause Iran to reconsider its rejection of diplomatic efforts, she said. Thursdays meeting in London came a day after US President Barack Obama warned Iran of growing isolation if its pursues nuclear weapons. It also followed talks in the British capital between Clinton and Russian Foreign Minister Sergei Lavrov, who said afterwards that Tehran cannot keep the world waiting forever in the standoff over its nuclear programme. Britain, China, France, Germany, Russia and the United States have been negotiating with Iran over its nuclear programme amid concerns that the Islamic republic is secretly developing fissile material for nuclear weapons. Under a UN plan, Iran-which says it only wants nuclear know-how for civilian purposes-would hand over most of its stocks of low-enriched uranium in return for French and Russian supplies of nuclear fuel enriched to the higher level required for a research reactor.